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In red wines, ciders and dark chocolate, just to name a few, complex plant compounds called procyanidins contribute to the taste and mouthfeel of a food or beverage—its perceived astringency and bitterness. But while food scientists have been able to assess the total content of procyanidins in a food or drink, they have not yet identified which specific procyanidins are present and correlate to specific perceptions.

But now, for the first time, a team led by researchers at Penn State has developed a method of "fingerprinting" procyanidins, introducing a more sophisticated and accurate way to analyze the perceptual variation in many foods and drinks.

"Drinking red wines, sometimes that tannic element is really harsh, like dragging sandpaper across your tongue, and sometimes it is velvety or smooth—and yet those two wines can have the same absolute amount of procyanidins, also referred to as condensed tannins," said team leader and senior author Misha Kwasniewski, associate research professor of fermented beverage science and technology in the College of Agricultural Sciences.

"We wanted to understand the biological activity of taste and mouthfeel, but this goes beyond taste and mouthfeel because procyanidins also are responsible for antioxidant activity and health-related benefits, and current analytical methods often show a lack of correlation with biological activities and health-related benefits."

According to Kwasniewski, current analytical methods only measure the total amount of procyanidins, rather than differentiate between them, so it can be difficult to determine how astringent a wine feels or how healthy a food might be. In a study published in the , the researchers described an advanced analytical chemistry method they named Condensed Tannin Fragmentation Fingerprinting. It is based on a technique known as in-source fragmentation, in which molecules from a food or beverage sample are identified using a laboratory device called a mass spectrometer.

Greatly simplified, the process first separates compounds in the sample. Then, different voltages are applied to break the procyanidins into fragments that the researchers can match to known standards, allowing them to identify and quantify each type of procyanidin.

In the study, the researchers tested the effectiveness and accuracy of their Condensed Tannin Fragmentation Fingerprinting method on 19 complex samples containing known amounts of various condensed tannins. The method demonstrated high accuracy and precision in characterizing the condensed tannins present, Kwasniewski said. Then the researchers used it to analyze eight commercially available ciders with similar results, validating the concept.

Now, Kwasniewski's research group is working with Pennsylvania winemakers to improve the quality of their products. In cool climates like Pennsylvania, he explained, wines tend not to have "as big a mouthfeel" as wines made from grapes grown in warmer climates—they have a less intense "dry" astringency profile.

"We want to learn how winemakers here—whether it be through new breeding programs and new grape varieties, or wine-making techniques or any number of interventions—can make the type of wines that they want to make, and sometimes that will be wines that have greater amounts of astringency," Kwasniewski said.

"The current methods that were available for understanding what was going on with the tannin structure really don't work with Pennsylvania wines."